The present invention generally relates to correcting optical errors of optical systems. More particularly, the present invention relates to improved methods and systems for planning and performing a sequence of corneal alterations in a laser surgery procedure for the correction of optical errors of eyes, wherein alterations associated with the correction of high-order optical aberrations are performed during latter stages of the procedure. The methods and systems of the present invention may be particularly well-suited for planning the treatment of eyes during in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), intrastromal reshaping of the cornea, and the like.
Many known laser eye surgery procedures employ an ultraviolet or infrared laser to remove a microscopic layer of stromal tissue from the cornea of the eye. The laser typically removes a selected shape of the corneal tissue, often to correct refractive errors of the eye. Ultraviolet laser ablation results in photodecomposition of the corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photo chemically, directly breaking the intermolecular bonds.
Laser surgery procedures can be used to alter the cornea for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. Control over the distribution of laser energy can be provided by a variety of systems and methods, including the use of ablative masks, fixed and moveable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like. In known systems, the laser beam often comprises a series of discrete pulses of laser light energy, with the total shape and amount of tissue impacted being determined by the shape, size, location, and number of laser-energy pulses impinging on the cornea. A variety of algorithms may be used to calculate the pattern of laser pulses used to alter the cornea so as to correct a refractive error of the eye. Known systems make use of a variety of forms of lasers and/or laser energy to effect the correction, including infrared lasers, ultraviolet lasers, femtosecond lasers, wavelength multiplied solid-state lasers, and the like. Alternative vision correction techniques make use of radial incisions in the cornea, intraocular lenses, removable corneal support structures, and the like.
Known corneal correction treatment methods have generally been successful in correcting standard vision errors, such as myopia, hyperopia, astigmatism, and the like. However, as with all successes, still further improvements are desirable. Toward that end, wavefront measurement systems are now available to accurately measure the refractive characteristics of a particular patient's eye. One exemplary wavefront technology system is the VISX WaveScan® System, which uses a Hartmann-Shack wavefront lenslet array that can quantify aberrations throughout the entire optical system of the patient's eye, including first- and second-order sphero-cylindrical errors, coma, and third and fourth-order aberrations related to coma, astigmatism, and spherical aberrations.
Wavefront measurement of the eye can be used to create an aberration map or wavefront elevation map that permits assessment of aberrations throughout the optical pathway of the eye, e.g., both corneal and non-corneal aberrations. Creation of the wavefront elevation map involves the determination of a surface that has gradients matching the gradients measured by the wavefront sensor array. The wavefront elevation map may then be used to compute a custom defect-correcting prescription for a surgical laser system to impose so as to treat (e.g., correct, alleviate, etc.) the complex aberrations of an eye. Known methods for creating a wavefront elevation map from measured wavefront data generally involve mathematically modeling using expansion series techniques. More specifically, Zernike polynomials have been employed to model the wavefront elevation map surface. Coefficients of the Zernike polynomials are derived through known fitting techniques. Alternatively, the wavefront elevation map may be created from measured wavefront data by direct integration techniques, as described by U.S. Pat. Nos. 7,168,807 and 7,175,278, the full disclosures of which are incorporated herein by reference.
Because of the complexity of high-order aberrations, they may be difficult to correct by using traditional means such as glasses or contact lenses or by conventional refractive surgery methods. However, in at least some instances, it may be possible to use customized laser eye surgery tailored to the particular combination of aberrations present in an eye to treat high-order aberrations.
In practice, the correction of high-order aberrations may result in under correction. Accordingly, it is desirable to provide optical treatments having increased effectiveness at treating high-order aberrations.